FIG. 11 is a schematic sectional view of a conventional light ring apparatus (JP281586 B). FIG. 12 is a sectional view taken along a line A-A in FIG. 11. FIG. 13 is a schematic front view showing a base of the conventional light ring apparatus and light emitting diodes installed on the base.
As shown in FIGS. 11 and 12, the light ring apparatus 30 is cylindrical and has nine chambers 31 formed at equal intervals and which are partitioned by three inclined triangular surfaces 31A. A vertex 32 of the triangular surfaces 31A of each chamber 31 is located at the outermost position of the central triangular surface 31A and at the outermost peripheral position of interior of the light ring apparatus 30. A tip portion of each light emitting diode 33 is placed substantially opposite the vertex 32 of the triangular surfaces. As shown in FIG. 12, if the triangular surfaces 31A are viewed from behind, ridge portions 34 and valley portions 35 all extending linearly are formed at equal intervals. Each chamber 31 functions as a light receiving surface that receives light from the corresponding light emitting diode 33. The chamber 31 sufficiently diffuses the light from the light emitting diode 33 and guides it to an upper portion 36 of the light ring apparatus 30. Then, the light guided into the upper portion 36 is introduced into a ring portion 37 and is viewed by a user.
Such an illumination apparatus requires two or more light emission sources in order to allow the ring portion 37 to emit light evenly. Further, there must be a long distance between the light emission sources and a ring-like illumination visible portion of an operation knob. Accordingly, if the light emission sources are arranged inside the operation knob, strict limitations are imposed on the arrangement and design of the parts.